"Organosilicon compound" is a generic term for compounds which generally contain one or more Si--C bonds. The organosilicon-related chemical industry is now growing rapidly, as typified by silicones (polyorganosiloxanes). Several processes are known for the preparation of organosilicon compounds. The following processes may be mentioned as representative ones: ##STR1##
The process (1) is the Rochow's direct process, in which an organosilicon compound is prepared directly from metallic silicon and a halogenated hydrocarbon. It is a process useful for the preparation of alkylchlorosilanes, which are the most important basic starting materials in the present organosilicon industry. As the halogenated hydrocarbons RCl, methyl chloride and chlorobenzene are used industrially. Other halogenated hydrocarbons give unduly low yields and, hence not, are suitable for industrial application.
On the other hand, the process (2) is a Grignard process while the process (3) is a dechlorination process making use of metallic sodium. These processes permit introduction of a desired alkyl group but Grignard reagents and metallic sodium are expensive and uneconomical.
The process (4) is a process similar to the present invention, but is accompanied by the serious problem that its raw material is limited to HSiCl.sub.3, CH.sub.3 SiHCl.sub.2 byproduced in the direct process, or the like.
Further, the processes (5) and (6) both involve high-temperature reactions and their raw materials are limited extremely, for example, to ##STR2## CH.sub.2 .dbd.CHCl, HSiCl.sub.3 and CH.sub.3 SiHCl.sub.2.
As has been mentioned above, basic raw materials of the present organosilicon industry are mostly methyl- or phenylchlorosilanes. Using these silicon compounds as starting raw materials, various functional materials such as silicones, silane coupling agents and silylating agents have been developed.
However, the conventional processes of the organosilicon industry, which employ chlorosilanes as basic raw materials, are generally accompanied by the following problems. First, process equipment is subjected to considerable corrosion since the raw materials contain chlorine and, hence, hydrogen chloride is given off. Second, the processes involve many reaction steps and are hence complex. Third, methylchlorosilanes are principally used due to a raw-material-related limitation and at least one of alkyl groups is a methyl group.
Regarding the synthesis of an alkylsilane or alkenylsilane by hydrosilylation (addition reaction) of SiH.sub.4 and an alkene or alkyne, there have been reported only a few research results because of difficulties in obtaining SiH.sub.4 and its high price. Included in such reports are Naturforsch, 56, 444 (1950); ibid., 76, 207 (1952); Z. Anorg. Allgem. Chem., 273, 275 (1953); J. Am. Chem. Soc., 76, 3897 (1954); and U.S. Pat. No. 2,786,862 (1957). According to these reports, the reaction temperatures were as high as 400.degree. to 500.degree. C. and the reactions were non-catalytic pyrolytic reactions. Furthermore, the yields were low and the selectivity to the resulting silane compounds was not controlled sufficiently. Absolutely no report has been made to date regarding hydrosilylation of Si.sub.2 H.sub.6 or Si.sub.3 H.sub.8.
The current principal application of silicon-containing polymers in the industry is as silicones (organopolysiloxanes). Their raw materials are alkylchlorosilanes produced by the reaction of metallic silicon and their corresponding halogenated hydrocarbons, namely, by the so-called direct process, in particular, dimethyldichlorosilane. Besides silicones, there are only a few practical application examples of silicon-containing polymers. The following silicon-containing polymers have been known by way of example:
(a) Permethylpolysilanes: ##STR3##
(b) Polysilastyrenes: ##STR4## wherein X is 0.8 to 1.3 and .phi. indicates a phenyl group. This same definition will hereinafter be applied.
(c) Polycarbosilanes: ##STR5##
(d) Polyvinylalkoxysilanes: ##STR6## The polymers (a) are prepared in a solvent such as xylene as shown by the following equation: ##STR7## This is also applied to the polymers (b). Although the polymers (a) are insoluble and infusible, the polymers (b) are soluble in solvents and thermoplastic. The polymers (c) are obtained by subjecting the polymers (a) to pyrolysis at high temperature and pressure, and are soluble in solvents and thermoplastic. The polymers (a), (b) and (c) are employed as ceramics binders, and the polymers (b) and (c) are employed as precursors for ceramics (SIC), especially, for ceramics (SIC) fibers ("NICARON", trade mark; product of Nippon Carbon Co., Ltd.).
The preparation of silicon-containing polymers, for example, the above-mentioned polymers (a), (b) and (c) from conventional alkylchlorosilanes as raw materials is however practiced in chlorine-containing systems so that the potential danger of corrosion of apparatus is involved. Moreover, their preparation processes are extremely complex. The polymers (d) are polymers of vinylsilane. The copolymers of vinylsilane with ethylene are used in a large volume for coating electrical wires and cables in the form of polyethylenes cross-linkable with water.
Polymers of alkenylsilanes have not been reported except for only one case in which allylsilane (CH.sub.2 .dbd.CH.dbd.CH.sub.2 --SiH.sub.3) was subjected to polymerization (anionic coordination polymerization) in the presence of a Ziegler catalyst [Journal of Polymer Science, 31, No. 122, 181(1958); Italian Patent No. 606,018].
Considerable technological development has been made with respect to silicon-containing ceramics in recent years. For example, silicon carbide (SiC), silicon nitride (Si.sub.3 N.sub.4), Cyalon, Si--Ti--C--O ceramics ("Tylano Fibers", product of Ube Industries, Ltd.), SiC--B.sub.4 C ceramics, Si.sub.3 N.sub.4 --SiC composite ceramics and the like have attracted attention as so-called fine ceramics.
Among these, silicon carbide is available in various forms such as powder, whiskers and fibers. It has been produced by various processes. For example, there are direct carbonization, reduction carbonization, vapor-phase synthesis, pyrolysis of silicon compounds, etc.
Direct carbonization comprises reduction of metallic silicon with coke at an elevated temperature (1400.degree. to 2600.degree. C.) and is hence economical. Fine silica SiO.sub.2 powder is however indispensable for obtaining fine SiC crystals excellent in sinterability. The reaction is exothermic and its control is hence difficult.
Reduction carbonization features reduction of SiO.sub.2 with coke. By reacting them at 1,500.degree. to 2,000.degree. C. in argon, .beta.-SiC is obtained. On the other hand, .alpha.-SiC is obtained by the Attison process which is similar to reduction carbonization. Reduction carbonization is employed principally these days in the industry.
In vapor-phase synthesis, a hydrocarbon is reacted with SiCl.sub.4, SiH.sub.4 or the like at 1,200.degree. C. or higher so that silicon carbide is obtained with high purity and in the form of ultrafine powder. However, the raw material is costly and the productivity is low.
Ceramics obtained by the above-described processes are all powdery. In order to obtain shaped products from them, it is hence necessary to press and process them in the presence of a sintering agent at elevated temperature and pressure. Their processing requires an extremely large press. In addition, limitations are imposed on their shaping and processing so that products of complex configurations can hardly be fabricated.
Pyrolysis of silicon compounds features easy processing, and also features pyrolyzing, as ceramics prepolymers, linear or cyclic silicon-containing high-molecular compounds having such recurring structural units as exemplified below:
(a) Permethylpolysilanes: ##STR8##
(b) Polysilastyrenes: ##STR9##
(c) Polycarbosilanes: ##STR10##
The polycarbosilanes are obtained by the pyrolysis of permethylpolysilanes or various organosilicon compounds, for example, tetramethylsilane, dimethyldichlorosilane and dodecamethylcyclohexasilane. They are fusible and also soluble in organic solvents such as benzene. As a polycarbosilane produced presently and industrially by pyrolysis, there are SiC fibers ("NICARON", trade mark; product of Nippon Carbon Co., Ltd.). The above fibers are produced in accordance with equations (A), (B) and (C) to be described below, by using as a starting material dimethyldichlorosilane obtained by the direct process. As high-strength fibers excellent in heat resistance, their future demand as a reinforcing material for resins, metals and ceramics is expected to increase [Chemistry Letters, 551, (1976); Japanese Patent Publication No. 26527/1982; Japanese Patent Publication No. 53892/1982; Japanese Patent Publication No. 38548/1982]. ##STR11##
It is the problem of the above process that the production steps are complex. Especially, in the step (A), the removal of unreacted sodium is cumbersome because metallic sodium is used in a solvent, and fractionation of polymers (separation and-removal of low molecular-weight polycarbosilanes) is required. In the reaction of the step (B), the reaction has to be carried out at high temperature and pressure (400.degree. C., 100 atm). In addition, the overall yield is low [especially, in the steps (B) and (C)], and free carbon and silica which are contained in at substantial levels in final products give deleterious effects to the physical properties of the final products.